Re: [PATCH] selftests: kvm: Adds a judgment on the return value

[David Hildenbrand]

Am 21.10.24 um 12:06 schrieb Liu Jing:
> The global variable errno is not recommended to be assigned,

Just curious: from where is that information?

Reading the man page:

"errno is defined by the ISO C standard to be a modifiable lvalue
 of type int, and must not be explicitly declared; errno may be a
 macro.  errno is thread-local; setting it in one thread does not
 affect its value in any other thread."

Paired with

"For some system calls and library functions (e.g.,
 getpriority(2)), -1 is a valid return on success.  In such cases,
 a successful return can be distinguished from an error return by
 setting errno to zero before the call"

Not objecting that relying on the rc looks cleaner.

>      and rc in the function does not check its return value, so it is fixed
>
> Signed-off-by: Liu Jing <liujing@xxxxxxxxxxxxxxxxxxxx>
> ---
>   tools/testing/selftests/kvm/s390x/cmma_test.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/s390x/cmma_test.c b/tools/testing/selftests/kvm/s390x/cmma_test.c
> index e32dd59703a0..c59c21f28bbd 100644
> --- a/tools/testing/selftests/kvm/s390x/cmma_test.c
> +++ b/tools/testing/selftests/kvm/s390x/cmma_test.c
> @@ -210,7 +210,7 @@ static int vm_get_cmma_bits(struct kvm_vm *vm, u64 flags, int *errno_out)
>   	struct kvm_s390_cmma_log args;
>   	int rc;
>   
> -	errno = 0;
> +	*errno_out = 0;
>   
>   	args = (struct kvm_s390_cmma_log){
>   		.start_gfn = 0,
> @@ -219,8 +219,10 @@ static int vm_get_cmma_bits(struct kvm_vm *vm, u64 flags, int *errno_out)
>   		.values = (__u64)&cmma_value_buf[0]
>   	};
>   	rc = __vm_ioctl(vm, KVM_S390_GET_CMMA_BITS, &args);
> +	if (rc < 0) {
> +		*errno_out = errno;
> +	}
>   

if (rc < 0)
	*errno_out = errno;

--
Cheers,

David / dhildenb